You have Strategy, but your execution Sucks. Because...

HBR dives into "Why Strategy Execution Unravels, and What to Do About It" - it's an ongoing project that has already covered 9 years, 40 experiments, 250 companies, and 4000 managers, and basically points out that a lot of the received wisdom on how to Execute on Strategy is, well, bullshit.
I strongly urge you to read the whole thing, but the TL;DR is basically the following

1. We Rool, You Suck: Individual teams (silos / business-units / whatever) can get very good at executing on Teh Strategy, but co-ordination across these units tends to suck. A lot.  For all the usual reasons...
2. Ignore von Moltke (**): Once Teh Strategy is in place, companies feel honor bound to stick to it, at all costs, and lack the agility to deviate based upon circumstances.
3. Speaking == Understanding: Management assumes that because they have explained Teh Strategy, everybody has understood, and internalized it.  Which, as it turns out, couldn't be further from the truth
4. A Players Rock: Too much emphasis on individual abilities & performance, while not recognizing the necessity of "soft skillz" like agility, teamwork, co-ordination, etc.
5. Hierarchy, FTW!: An emphasis on top-down execution, instead of promoting leadership skills across the organization.

 While some of these tend to be more specific to large companies - small companies tend to be less likely to have dysfunctional inter-team communication - others are particularly prevalent in small companies.  Heck, the "A Players Rock" approach to existence is almost a mantra in the Silicon Valley culture, no?

Anyhow, go read the article, it is simultaneously depressing, and eye-opening.

(**)